Why I dont's see colors in object mode?
You are in solid viewport shading mode.

Look at the header of the 3D View and locate the four spheres. There you can change the viewport shading mode.

When you are in Solid shading mode, the color in the 3D viewport is from the materials Viewport Display > Color. When you are not using nodes (as with your red cube), then the material's Base Color is the same as the Viewport Display > Color.



However, when you activate nodes, the rendering settings (defined in the nodes) and the Viewport Display settings are not synchronized anymore.



To preview the material settings and material nodes, switch the viewport to material preview by clicking on the third sphere in the header of the 3D viewport.